Heat dissipation device and fan module thereof

ABSTRACT

An exemplary fan module includes a main fan and an assist fan. The main and assist fans each include a rotor which includes a hub and a plurality of blades around the hub. The assist fan is located below the hub of the main fan. Inner sides of the blades of the assist fan adjacent to the hub of the assist fan are located within a range of a radius of the hub of the main fan along a radial direction of the rotor of the main fan. Outer sides of the blades of the assist fan away from the hub of the assist fan are located beyond the hub of the main fan along the radial direction of the rotor of the main fan. The blades of the assist fan are pushed to rotate by airflow from the main fan to produce airflow towards a heat sink.

CROSS-REFERENCE TO RELATED APPLICATION

This application is related to a co-pending application entitled “FAN MODULE AND HEAT DISSIPATION DEVICE INCORPORATING THE SAME” (attorney docket number US 30707), assigned to the same assignee of this application and filed on the same date.

BACKGROUND

1. Technical Field

The disclosure generally relates to heat dissipation, and particularly to a heat dissipation device having an improved fan module.

2. Description of Related Art

A typical heat dissipation device includes a heat sink and a cooling fan arranged on the heat sink. Electronic components are usually attached to a central portion of the heat sink, the location at which heat generated by the electronic component is primarily concentrated. The cooling fan includes an impeller. The impeller includes a hub and a plurality of blades around the hub. During operation of the cooling fan, the impeller rotates and produces airflow towards the heat sink. However, due to blocked access to the hub of the impeller, only a small portion of the airflow reaches the central portion of the heat sink immediately under the hub, such that heat concentrated at the central portion of the heat sink cannot be efficiently dissipated.

What is needed, therefore, is a heat dissipation device and a fan module of the heat dissipation device which can overcome the described limitations.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the present embodiments can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present embodiments. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views.

FIG. 1 is a cross sectional, schematic view of a heat dissipation device in accordance with a first embodiment of the disclosure.

FIG. 2 is an enlarged view of a fan module of the heat dissipation device of FIG. 1.

FIG. 3 is a cross sectional, schematic view of a fan module of a heat dissipation device in accordance with a second embodiment of the disclosure.

DETAILED DESCRIPTION

Referring to FIG. 1, a heat dissipation device in accordance with a first embodiment is shown. The heat dissipation device is mounted on an electronic component 10, such as a central processing unit (CPU), for dissipating heat therefrom. The heat dissipation device includes a heat sink 20 and a fan module 30 arranged on the heat sink 20.

The heat sink 20 includes a substrate 21 and a plurality of fins 23 extending perpendicularly up from the substrate 21. The substrate 21 is attached to the electronic component 10 at a central portion of a bottom surface thereof. The fins 23 are parallel to and spaced from each other. An air channel 231 is defined between every two adjacent fins 23. The fins 23 includes a plurality of inner fins 234 at a central portion of the heat sink 10, and a plurality of outer fins 236 around the inner fins 234. The inner fins 234 each have a length less than that of the outer fins 236, and therefore a recess 232 is defined in the central portion of the heat sink 20 over the inner fins 234.

The fan module 30 includes a main fan 31 and an assist fan 33 located below the main fan 31. The main and assist fans 31, 33 are axial fans.

Referring to FIG. 2, the main fan 31 includes a frame 311, a bearing system 313, a stator 315 mounted on the frame 311, and a rotor 317 covering the stator 315.

The frame 311 is mounted on the outer fins 236 of the heat sink 20. The frame 311 is substantially rectangular and hollow. The frame 311 defines an air inlet 3111 at a top end thereof, and an air outlet 3112 at a bottom end thereof. A base 3113 is formed at a central portion of the bottom end of the frame 311. The base 3113 is connected to the frame 311 via a plurality of ribs (not labeled). The air outlet 3112 is defined between the ribs. A central tube 3114 extends perpendicularly up from a central portion of the base 3113.

The bearing system 313 is received in the central tube 3114 of the frame 311. The bearing system 313 includes a sleeve 3131 and a locking ring 3132 located below the sleeve 3131. The sleeve 3131 is hollow and cylindrical, and the locking ring 3132 is annular.

The stator 315 includes a circuit board 3151 and a coil assembly 3152 located on the circuit board 3151. The circuit board 3151 and the coil assembly 3152 are mounted around the central tube 3114 of the frame 311.

The rotor 317 is rotatably mounted around the coil assembly 3152 of the stator 315. The rotor 317 includes a hub 3171, a shaft 3172, a plurality of blades 3173, and a magnet 3174. The hub 3171 is semi-enclosed, and includes a top wall 3175 and a sidewall 3176 extending perpendicularly down from an outer periphery of the bottom wall 3175. A top end of the shaft 3172 is fixed at a central portion of the top wall 3175 of the hub 3171. A middle portion of the shaft 3172 is received in the sleeve 3131. A bottom end of the shaft 3172 defines an annular notch 3177 engaged with the locking ring 3132 to limit floating of the rotor 317. The rotor 317 with the shaft 3172 is rotatable with respect to the bearing system 313. The blades 3173 extend radially out from an outer circumferential surface of the sidewall 3176 of the hub 3171. The magnet 3174 is annular, and contacted with an inner circumferential surface of the sidewall 3176 of the hub 3171.

The assist fan 33 is located under the hub 3171 of the main fan 31, and received in the recess 232 of the heat sink 20. The assist fan 33 has an outer diameter less than that of the main fan 31. The assist fan 33 includes a frame 331, a bearing system 333, and a rotor 337.

The frame 331 of the assist fan 33 is mounted on the inner fins 234 of the heat sink 20. The frame 331 has an outer diameter less than that of the frame 311 of the main fan 31, and slightly larger than an outer diameter of the sidewall 3176 of the hub 3171 of the main fan 31. The frame 331 is also substantially rectangular and hollow. The frame 331 defines an air inlet 3311 at a top end thereof, and an air outlet 3312 at a bottom end thereof. A base 3313 is formed at a central portion of the bottom end of the frame 331. The base 3313 is connected to the frame 331 via a plurality of ribs (not labeled). The air outlet 3312 is defined between the ribs. A central tube 3314 extends perpendicularly up from a central portion of the base 3313.

The bearing system 333 is the same as the bearing system 313 of the main fan 31 except in dimensions. The bearing system 333 also includes a sleeve 3331 and a locking ring 3332 located below the sleeve 3331.

The rotor 337 is rotatably mounted around the central tube 3314 of the frame 331. The rotor 337 includes a hub 3371, a shaft 3372, and a plurality of blades 3373. The hub 3371 has an outer diameter much less than that of the hub 3171 of the main fan 31. The hub 3371 also includes a top wall 3375 and a sidewall 3376 extending perpendicularly down from an outer periphery of the top wall 3375. A top end of the shaft 3372 is fixed to a central portion of the top wall 3375 of the hub 3371. A middle portion of the shaft 3372 is received in the sleeve 3331. A bottom end of the shaft 3372 defines an annular notch 3377 engaged with the locking ring 3332 to limit floating of the rotor 337. The rotor 337 with the shaft 3372 is rotatable with respect to the bearing system 333. The blades 3373 extend radially out from an outer circumferential surface of the sidewall 3376 of the hub 3371. Inner sides of the blades 3373 of the assist fan 33 adjacent to the hub 3371 are located within a range of a radius of the hub 3171 of the main fan 31 along a radial direction of the rotor 317 of the main fan 31. Outer sides of the blades 3373 of the assist fan 33 away from the hub 3371 are located beyond the hub 3171 of the main fan 31 along the radial direction of the rotor 317 of the main fan 31. This ensures that airflow from the main fan 31 is capable to flow towards outer portions of the blades 3373 of the assist fan 33 beyond the hub 3171 of the main fan 31, and therefore pushes the rotor 337 of the assist fan 33 to rotate.

During operation, the rotor 317 of the main fan 31 of the fan module 30 rotates and thus produces airflow. A portion of the airflow from the main fan 31 flows towards the outer fins 236 of the heat sink 20 via the air outlet 3112 of the main fan 31, and then enters corresponding air passages 231 between the outer fins 236, thereby taking heat away. Another portion of the airflow from the main fan 31 flows towards the blades 3373 of the assist fan 33 via the air outlet 3112 of the main fan 31 and the air inlet 3311 of the assist fan 33, and therefore pushes the rotor 337 of the assist fan 33 to rotate to produce airflow. The airflow from the assist fan 33 flows towards the inner fins 234 of heat sink 20 via the air outlet 3312 of the assist fan 33, and then enters corresponding air passages 231 between the inner fins 234 of heat sink 20, thereby taking away the heat concentrated at the central portion of the heat sink 20.

In the present heat dissipation device, the assist fan 33 is located below the hub 3171 of the rotor 317 of the assist fan 31. The inner sides of the blades 3373 adjacent to the hub 3371 of the assist fan 33 are located within the range of the radius of the hub 3171 of the main fan 31 along the radial direction of the rotor 317 of the main fan 31. Outer sides of the blades 3373 away from the hub 3371 of the assist fan 33 are located beyond the hub 3171 of the main fan 31 along the radial direction of the rotor 317 of the main fan 31. The blades 3373 of the rotor 337 of the assist fan 33 are pushed to rotate by the airflow from the main fan 31, and therefore produce airflow towards the central portion of the heat sink 20. Thus, heat concentrated at the central portion of the heat sink 20 can be efficiently dissipated by the assist fan 33. This prevents the electronic component 10 at the central portion of the substrate 21 of the heat sink 20 from overheating. In addition, the blades 3373 of the rotor 337 of the assist fan 33 are pushed to rotate by the airflow from the main fan 31. Therefore, a stator and a magnet are not required in the assist fan 33. The hub 3371 of the assist fan 33 is reasonably smaller than the hub 3171 of the main fan 31, and a blocked access to the hub 3371 of the assist fan 33 is relatively smaller. Thus, an airflow dead area under the hub 3171 of the main fan 31 is reduced, and the heat dissipation efficiency of the heat dissipation device is improved.

Referring to FIG. 3, a fan module 30 a of a heat dissipation device in accordance with a second embodiment is shown. The fan module 30 a of the second embodiment differs from the fan module 30 of the first embodiment only in the assist fan.

In this embodiment, there is no frame in an assist fan 33 a of the fan module 30 a. A bearing system 333 a of the assist fan 33 a is received in a hub 3371 a of a rotor 337 a of the assist fan 33 a, with a sleeve 3331 a of the bearing system 333 a of the assist fan 33 a fixed to an inner circumferential surface of the hub 3371 a of the rotor 337 a of the assist fan 33 a. A shaft 3372 a of the assist fan 33 a is coaxial to the shaft 3172 of the main fan 31. A top end of the shaft 3372 a of the assist fan 33 a is fixed at a central portion of a bottom surface of the base 3113 of the main fan 31. A middle portion of the shaft 3372 a is received in the sleeve 3331 a of the bearing system 333 a. A bottom end of the shaft 3372 a defines an annular notch 3377 a engaged with a locking ring 3132 a of the bearing system 333 a, and thus the hub 3371 a of the assist fan 33 a is rotatable with respect to the shaft 3372 a. During operation, a portion of the airflow form the main fan 31 flows towards the blades 3373 a of the assist fan 33 a, and pushes the rotor 337 a and the bearing system 333 a of the assist fan 33 a to rotate around the shaft 3372 a, thereby producing airflow towards the central portion of the heat sink 20.

In the present fan module 30 a, the frame is omitted, and thus, a size of the hub 3371 a of the assist fan 33 a in this embodiment can be further reduced relative to the first embodiment, and therefore a blocked access to the hub 3371 a of the assist fan 33 a is relatively smaller. Thus, the airflow dead area under the hub 3171 of the main fan 31 is reduced, and the heat dissipation efficiency of the heat dissipation device is further improved.

It is to be understood, however, that even though numerous characteristics and advantages of the present embodiments have been set forth in the foregoing description, together with details of the structures and functions of the embodiments, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed. 

1. A fan module, comprising: a main fan comprising a rotor, the rotor of the main fan comprising a hub and a plurality of blades around the hub; and an assist fan located below the hub of the main fan, the assist fan comprising a rotor, the rotor of the assist fan comprising a hub and a plurality of blades around the hub, inner sides of the blades of the assist fan adjacent to the hub of the assist fan being located within a range of a radius of the hub of the main fan along a radial direction of the rotor of the main fan, outer sides of the blades of the assist fan away from the hub of the assist fan being located beyond the hub of the main fan along the radial direction of the rotor of the main fan, the blades of the assist fan pushed to rotate by airflow from the main fan to produce airflow.
 2. The fan module of claim 1, wherein the assist fan further comprises a bearing system and a shaft, the bearing system of the assist fan fixed in the hub of the rotor of the assist fan, a top end of the shaft of the assist fan fixed on the main fan, the rotor and the bearing system of the assist fan being rotatable with respect to the shaft of the assist fan.
 3. The fan module of claim 2, wherein the main fan further comprises a base supporting the rotor of the main fan, the top end of the shaft of the assist fan fixed on the base of the main fan.
 4. The fan module of claim 2, wherein the bearing system of the assist fan comprises a sleeve and a locking ring located below the sleeve, the sleeve fixed on an inner circumferential surface of the hub of the rotor of the assist fan, a middle portion of the shaft of the assist fan received in the sleeve, a bottom end of the shaft of the assist fan defining a notch engaged with the locking ring of the bearing system of the assist fan.
 5. The fan module of claim 1, wherein the assist fan further comprises a base and a bearing system, a central tube extending upwardly from the base of the assist fan, the bearing system of the assistant fan received in the central tube of the assistant fan, the rotor of the assist fan further comprising a shaft with a top end fixed on the hub of the rotor of the assist fan, and a bottom end rotatably mounted in the bearing system.
 6. The fan module of claim 5, wherein the hub of the rotor of the assist fan is disposed around the central tube.
 7. The fan module of claim 5, wherein the bearing system of the assist fan comprises a sleeve and a locking ring located below the sleeve, a middle portion of the shaft of the assist fan received in the sleeve, a bottom end of the shaft of the assist fan defining a notch engaged with the locking ring of the bearing system of the assist fan.
 8. The fan module of claim 1, wherein the main fan defines an air outlet at a bottom end thereof, airflow from the main fan flowing towards the blades of the rotor of the assist fan via the air outlet of the main fan.
 9. The fan module of claim 1, wherein the assist fan has an outer diameter less than that of the main fan.
 10. A heat dissipation device, comprising: a heat sink; and a fan module arranged on the heat sink, the fan module comprising: a main fan comprising a rotor, the rotor of the main fan comprising a hub and a plurality of blades around the hub; and an assist fan located below the hub of the main fan, the assist fan comprising a rotor, the rotor of the assist fan comprising a hub and a plurality of blades around the hub, inner sides of the blades of the assist fan adjacent to the hub of the assist fan being located within a range of a radius of the hub of the main fan along a radial direction of the rotor of the main fan, outer sides of the blades of the assist fan away from the hub of the assist fan being located beyond the hub of the main fan along the radial direction of the rotor of the main fan, the blades of the assist fan pushed to rotate by airflow from the main fan to produce airflow.
 11. The heat dissipation device of claim 10, wherein the heat sink defines a recess in a central portion thereof, the assist fan of the fan module received in the recess.
 12. The heat dissipation device of claim 10, wherein the assist fan further comprises a bearing system and a shaft, the bearing system of the assist fan fixed in the hub of the rotor of the assist fan, a top end of the shaft of the assist fan fixed on the main fan, the rotor and the bearing system of the assist fan being rotatable with respect to the shaft of the assist fan.
 13. The heat dissipation device of claim 12, wherein the main fan further comprises a base supporting the rotor of the main fan, the top end of the shaft of the assist fan fixed on the base of the main fan.
 14. The heat dissipation device of claim 12, wherein the bearing system of the assist fan comprises a sleeve and a locking ring located below the sleeve, the sleeve fixed on an inner circumferential surface of the hub of the rotor of the assist fan, a middle portion of the shaft of the assist fan received in the sleeve, a bottom end of the shaft of the assist fan defining a notch engaged with the locking ring of the bearing system of the assist fan.
 15. The heat dissipation device of claim 10, wherein the assist fan further comprises a base and a bearing system, a central tube extending upwardly from the base of the assist fan, the bearing system of the assistant fan received in the central tube of the assistant fan, the rotor of the assist fan further comprising a shaft with a top end fixed on the hub of the rotor of the assist fan, and a bottom end rotatably mounted in the bearing system.
 16. The fan module of claim 15, wherein the hub of the rotor of the assist fan is disposed around the central tube.
 17. The fan module of claim 15, wherein the bearing system of the assist fan comprises a sleeve and a locking ring located below the sleeve, a middle portion of the shaft of the assist fan received in the sleeve, a bottom end of the shaft of the assist fan defining a notch engaged with the locking ring of the bearing system of the assist fan.
 18. The fan module of claim 10, wherein the assist fan has an outer diameter less than that of the main fan. 